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The role of biofilms in fossil preservation, Florissant Formation, Colorado

By
Neal R. O'Brien
Neal R. O'Brien
1
Department of Geology, State University of New York at Potsdam, Potsdam, New York 13676, USA
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Herbert W. Meyer
Herbert W. Meyer
2
National Park Service, Florissant Fossil Beds National Monument, P.O. Box 185, Florissant, Colorado 80816, USA
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Ian C. Harding
Ian C. Harding
3
School of Ocean and Earth Science, National Oceanography Centre, Southampton, University of Southampton, European Way, Southampton, England SO14 3 ZH, UK
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Published:
January 01, 2008

Scanning electron microscopy (SEM) of insect and plant fossils in the lacustrine shales of the Eocene Florissant Formation of Florissant, Colorado, was used to investigate the mechanisms of fossil preservation. The fossiliferous Florissant “paper shales” are composed of thin laminae of diatomite that form couplets with alternating smectitic clay laminae. The millimeter-scale sedimentary couplets may preserve an episodic record of sedimentation and are interbedded with less frequent, coarser volcaniclastic layers. The insect and plant fossils are associated with biofilms of extracellular polymeric substances (EPS) secreted by diatoms. The preserved organisms are entangled in the diatom aggregates coated with the EPS biofilm. We suggest that decomposition of the organisms was arrested during sedimentation and burial by the protective nature of the mucus covering, the properties of which limited the actions of bacteria and grazers and may have enhanced fossilization. A novel contribution of the study is a demonstration that this mechanism of exceptional preservation is also common at other similar lacustrine fossil sites, as supported by a further SEM analysis of insect and plant fossils from other Cenozoic lake deposits formed in environments comparable to the Floris-sant Formation. The deposits include the Oligocene shale at Canyon Ferry, Montana; the Miocene Savage Canyon Formation, Stewart Valley, Nevada; and the Miocene Shanwang Beds of Shandong Province in northeast China. In addition, cultures of diatomaceous biofilms, grown in the laboratory display morphological features identical to those of the fossil diatomaceous biofilms. Our contribution indicates the significance of biofilms in fossil preservation at Florissant and other deposits.

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GSA Special Papers

Paleontology of the Upper Eocene Florissant Formation, Colorado

Herbert W. Meyer
Herbert W. Meyer
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Dena M. Smith
Dena M. Smith
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Geological Society of America
Volume
435
ISBN print:
9780813724355
Publication date:
January 01, 2008

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